The only time I disengage the auto-muck is when I'm sitting on the BB with a monster (JJ+/AK) and it looks like it'll get folded to me. Doing the same with utter crap (72o) is nice, too.
It gives them absolutely no information about how I play, but it could mislead them if they don't understand that showing them AA (or whatever) doesn't change my odds
of getting AA the next hand. Or if they mistake me for being on tilt because it got folded to me with a monster.
All other times it's an auto-muck for me.
If someone folds to my river-bet and asks "what did you have?" my answer is always "now you'll never know". Can potentially put them on tilt.